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Image of the Week

Prediction of astrometric microlensing events during the Gaia mission

Proft et al., in their paper (2011A&A...536A..50P) titled "Prediction of astrometric microlensing events during the Gaia mission" identify stars with large proper motions that are potential candidates for the astrometric microlensing effect during the Gaia mission. The effect allows a precise measurement of the mass of a single star that is acting as a lens. They construct a candidate list by combining information from several input catalogs including PPMXL, LSPM, PPMX, OGLEBG, and UCAC3. The selection of the microlensing candidates includes the verification of their proper motions as well as the calculation of the centroid shift of the source resulting from the astrometric microlensing effect. The assembled microlensing catalog comprises 1118 candidates for the years 2012 to 2019. The analysis demonstrates that 96% of the (high) proper motions of these candidates are erroneous. They are thus left with 43 confirmed candidates for astrometric microlensing during the expected Gaia mission. For most of them the light centroid shift is below ~100 µas (assuming a dark lens) or the astrometric deviation is considerably reduced by the brightness of the lens. Due to this the astrometric microlensing effect can potentially be measured for nine candidates that have a centroid shift between 100 and 4000 µas. For two of these astrometric microlensing candidates they predict a strong centroid shift of about 1000 and 4000 µas, respectively, that should be observable over a period of a few months up to a few years with the Gaia mission.

In the plot you can see the distribution of all 1118 supposed microlensing candidates. The 1075 spurious candidates (yellow dots), the 43 real candidates (blue triangles, red circles, and green squares) and the 9 best microlensing events (red circles and green squares) are represented in Galactic coordinates (Aitoff projection). The 2 events that should be observable with Gaia are plotted as green squares. The majority of microlensing candidates and possible events are close to the Galactic plane.